Old age and obesity are prevalent risk factors for morbidity and mortality. Weight loss (WL) ameliorates many clinical consequences of obesity; yet despite its benefits, recommendation of intentional WL in older adults remains controversial. Reluctance stems, at least in part, from loss of bone mass known to accompany overall WL and the potential for exacerbation of age-related risk of osteoporosis and fracture. Addition of aerobic exercise to WL may be an effective means to attenuate, but not stop, WL-associated reductions in bone mineral density (BMD). Resistance exercise alone, or when combined with aerobic exercise, has also shown protective effects on BMD loss during moderate WL in older adults. However, a study directly comparing the effect exercise modality (aerobic versus resistance) during WL on changes in BMD and other measures of bone quality (i.e. strength, structure, and turnover) in overweight and obese, older adults has yet to be done. This is an understudied research area of great scientific need. Thus, the main research objective of this Mentored Research Scientist Development Award (MRSDA) is to generate data that will inform future R-level awards, led by the candidate, in the identification of WL strategies that minimize bone loss and subsequent fracture risk in overweight and obese, older adults. We hypothesize that resistance exercise will reduce the loss of bone density and quality associated with WL in overweight and obese, older adults when compared to aerobic exercise or WL alone. If confirmed, findings have the potential to influence recommendations for physical exercise and WL in this population. The main training objective of this MRSDA is to meet the PI's immediate career goal by providing her with skill in the design and conduct of behavioral based WL- interventions as well as in-depth knowledge of the effect of WL strategies on bone density and quality in older adults, offering the necessary accompaniment to the candidate's previous NRSA- supported postdoctoral work studying the effects of WL-associated fat and lean mass loss on cardiometabolic risk and physical function in older adults. The proposed training plan features an exceptional mentoring team and training environment, with content mentors in the areas of healthy aging, behavioral based WL-interventions, and bone metabolism, as well as carefully selected didactic and hands-on training in bone physiology, image analysis, and laboratory techniques. Completion of the activities outlined in this MRSDA will allow the PI to achieve her long-term career goal as independent clinical investigator, with the ability to comprehensively identify of optimal WL therapies to promote and preserve functional independence in overweight and obese, older adults.